Recently, a large number of solar cells are produced because of growing awareness of importance of utilizing natural energy. And some cases are reported where solar cells get out of order or get in trouble such as decrease of output power because of aging degradation. So, some fault diagnosis methods for diagnosing solar cells have been developed.
For example, a fault diagnosis method for diagnosing a photovoltaic string having pluralities of photovoltaic modules connected in series is described in Patent Literature 1. This method requires two configuration of the first configuration where a signal generator and a waveform observer are connected to one end of a normal photovoltaic string with the other end being open end, and the second configuration where a signal generator and a waveform observer are connected to one end of a photovoltaic string under test. A difference signal is obtained by the difference between an observation signal (an output signal reflected out of the photovoltaic string) by the waveform observer in the first configuration and an observation signal by the waveform observer in the second configuration. Given that the time point when rising of the difference signal exceeds a threshold is denoted by Ta, that the time point when falling of the difference signal exceeds a threshold is denoted by Tb, and that the distance from the signal generator to the open end in the second configuration is denoted by LA, the distance Lc from the signal generator to the fault location is obtained by Lc=(Ta/Tb)*LA.